1. Field of the Invention
This invention relates to a signal processing method in autoradiography.
2. Description of the Prior Art
Autoradiography has been known as a method for obtaining locational information on radioactively labeled substances distributed in at least one dimensional direction to form a row on a support medium.
For instance, the autoradiography comprises steps of: labeling organism-originating biopolymers such as proteins or nucleic acids with a radioactive element; resolving the radioactively labeled biopolymers, derivatives thereof, or cleavage products thereof (referred to hereafter as "radioactively labeled substances") on a gel support (support medium) through a resolving process such as electrophoresis to form a resolved pattern of the radioactively labeled substances (the resolved pattern is not visible); placing said gel support and a high-sensitivity type X-ray film together in layers for a certain period of time to expose said film and developing said film to give the autoradiograph of the resolved pattern as a visible image on the film; and obtaining the locational information of the radioactively labeled substances from said visible image. Further, the identification of the polymeric substances, determination of molecular weight of the polymeric substances and isolation of the polymeric substances can be obtained based on the observed locational information. Such autoradiography has been effectively utilized for determining the base sequence of nucleic acids such as DNA or the like.
In the conventional autoradiography utilizing the above-described radiographic process, visualization of the autoradiograph having the locational information on radioactively labeled substances on a radiographic film is essentially required.
Investigators generally analyze the distribution of the radioactively labeled substances on a support medium through study of the visualized autoradiograph. Further, the visually-obtained locational information on the radioactively labeled substances is generally subjected to various analyses to study the characteristics and functions of the radioactively labeled substance.
Since the conventional autoradiography requires visual analysis of the autoradiograph, there is a drawback in that the locational information on the radioactively labeled substances obtained by analysis of the visualized autoradiograph varies or fluctuates depending on the skill of investigators, and the accuracy of the information is limited to a certain extent. Particularly, when the autoradiograph visualized on a radiographic film shows an image of reduced quality (in regard of sharpness, contrast, etc.), satisfactory information can be hardly obtained and the accuracy is low. In order to improve the accuracy of the locational information, for instance, a visualized autoradiograph can be scanned with a device such as a scanning densitometer. However, such a scanning process requires increased operation time and complicated procedures. Further, there is a limitation on the increase of the accuracy obtainable when using the device.
For instance, in carrying out the exposing procedure, the support medium carrying the above-mentioned resolved rows thereon and the radiograph film sometimes cannot be accurately arranged together in layers. In such case, the resolved rows, namely, rows of resolved substances (e.g., electrophoretic rows) visualized on the radiographic film are not parallel to the longitudinal direction of the film and thus give a dislocated pattern. As a result, error is introduced into the visual analysis of the locational information on the radioactively labeled substances to decrease the accuracy thereof.
Further, the rows of the resolved radioactively labeled substances on the support medium are sometimes non-parallel to the longitudinal direction of the support medium or distorted, depending on the kind of support medium or resolving conditions. For instance, a gel support medium is generally held between two glass plates in the resolving procedure because the gel lacks a self-supporting property. As a result, the gel occasionally becomes uneven in the thickness due to deformation of the covers (i.e. the glass plates) and accordingly the radioactively labeled substances are not always resolved uniformly on the gel. The lack of uniformity of the resolved pattern is also caused by air foams contained in the gel or by heterogeneous dispersion of the composition of the gel. For these reasons, a phenomenon known as the so-called smiling effect is often observed. In this phenomenon, the migration distance of the resolved row in the vicinity of the center of the support medium is longer than the migration distances on the both sides thereof. Additionally, in electrophoresis, the voltage sometimes is not applied uniformly to the support medium and in that case the resolving conditions are made locally uneven on the support medium and consequently the resolved rows obtained are distorted.
Furthermore, when radioactively labeled impurities such as natural radioactive materials are contained in the sample, the support medium is contaminated with such radioactive impurities or the resolution conditions are otherwise not appropriate such that a noise sometimes appears on the autoradiograph. In consequence, accurate analysis of the locational information on the radioactively labeled substances becomes difficult, resulting in decrease of accuracy of the desired information.
In the above-described cases, it is not easy to analyze the locational information on the radioactively labeled substances. Thus, even if the aforementioned additional detection device is used, it is still difficult to obtain satisfactorily accurate locational information on the radioactively labeled substances.